Figure 2.

Sustained STAT3 expression induces sprouting of lesioned and unlesioned fibres in the cervical spinal cord following injury. (A,B) Confocal images of p-STAT3 expression in layer V cortical neurons (green, NeuroTrace 435; red, p-STAT3) of mice injected with Control rAAV (A) or rAAV-STAT3 (B) and perfused 3 w following a mid thoracic hemisection. Arrows indicate p-STAT3-positive neurons (magnified in insets). (C) Confocal images of p-STAT3 expression in hindlimb CST projection neurons that were retrogradely labelled from the lesion site (blue, neurons retrogradely labelled with dextran tetramethylrhodamine; green, NeuroTrace 435; red, p-STAT3) in mice injected with rAAV-STAT3 and perfused 3 w following a mid thoracic hemisection. (D) Quantification of p-STAT3 expression in layer V neurons in the transduced area of the hindlimb motor cortex of unlesioned mice (left panel) either untreated (C same as in Fig 1E) or injected with rAAV-STAT3 (red bar) and lesioned mice (right panel, perfused 3 w after injury) injected with Control rAAV (grey bar) or rAAV-STAT3 (red bar, n=3–5 mice per group). (E) Quantification of p-STAT3 expression in hindlimb CST projection neurons that were retrogradely labelled from the lesion site in mice injected with rAAV-STAT3 (n=4). (F) Schematic representation of the analysis of cervical CST sprouting and remodelling following a mid thoracic spinal cord injury. (G,H) Confocal images of cervical hindlimb CST collaterals in lesioned mice injected with Control rAAV (G) or rAAV-STAT3 (H) and perfused 3 w following injury. Arrows indicate collaterals as they exit into the grey matter. (I,J) Quantification of the number of collaterals exiting the hindlimb CST in the cervical spinal cord (I) and of the percentage of long propriospinal neurons contacted by CST fibres (J) in mice injected with Control rAAV (grey bars, n=9) or rAAV-STAT3 (red bars, n=9) 3 w following spinal cord injury. (K) Schematic representation of the analysis of cervical CST sprouting and remodelling in unlesioned mice. (L,M) Confocal images of cervical hindlimb CST collaterals in unlesioned mice injected with Control rAAV (L) or rAAV-STAT3 (M). (N,O) Quantification of the number of collaterals exiting the hindlimb CST in the cervical spinal cord (N) and of the percentage of long propriospinal neurons contacted by CST fibres (O) in unlesioned mice injected with Control rAAV (grey bars, n=5) or rAAV-STAT3 (red bars, n=8). All bars and error bars in this figure represent mean±s.e.m. Statistical analysis was performed using t-tests. *P<0.05; ***P<0.001. Scale bar equals 50 μm in B (also for A), 25 μm in C and 50 μm in H (also for G,L,M). CST, corticospinal tract; rAAV, recombinant adeno-associated viruses; SC, spinal cord; STAT3, signal transducer and activator of transcription 3.